Well then I guess I can explain the game...
Diplomacy is set in World War I, and there are 7 playable countries: England, France, Germany, Russia, Austria-Hungary, Turkey, and Italy. Each starts with 1 naval unit and 2 army units (except for Russia, who has 2 naval and 2 army units, to compensate for its size, and England, which has 2 naval units and 1 army unit to compensate for it being an island). Then you try and take over the world (like all great games).
Each turn, you all write down your orders for your units, and place them in a hat to be read all at once (turns are done at the same time, not one at a time). You often have to work together with other players to gain support for attacks. Each player also has "supply centers", which must be controlled to maintain your units. When you gain more supply centers, you gain more units.
Example: England wants to move into a territory, they say "Army-Territory A TO Territory B". If there is another unit already in Territory B, the move fails. Unless England (or another player) says "Army-Territory C SUPPORTS Army-Territory A TO Territory B". Then, since there is 1 army with support from another army, the army from Territory A is able to move to Territory B.
Basically, it is a game that forces you to work with other players, but also creates an atmosphere for telling one person you're going to do one thing, to gain their support, while also stabbing them in the back on the same turn.